The present invention relates to an optical storage apparatus using an exchangeable medium such as CD, MO cartridge, or the like and, more particularly, to an optical storage apparatus for variably controlling a medium rotational speed for a constant linear velocity (CLV) and simultaneously correcting an eccentricity by using an eccentricity memory when a CD is reproduced.
Attention is paid to an optical disk as a storage medium as a center of multimedia which has rapidly been developing in recent years. For example, as for an MO cartridge of 3.5 inches, in addition to conventional MO cartridges of 128 MB and 230 MB, media of a high density recording such as MO cartridges of 540 MB and 640 MB and, further, a medium of a direct overwriting type are also being provided in recent years. As an optical disk drive, therefore, it is desirable that various media of 128 MB, 230 MB, 540 MB, and 640 MB, and further of the direct overwriting type which can be obtained at present can be used. In recent years, in personal computers which have rapidly been spread, a function for reproducing a compact disc (CD) which is known as a read only disk is indispensable. It is difficult to mount an optical disk drive of an MO cartridge as an exchangeable optical disk drive in addition to an optical disk drive for a CD from a viewpoint of a space and costs. In recent years, therefore, an optical disk drive which can use both of the MO cartridge and the CD has also been developed. According to the optical disk drive of the CD/MO compatible type, with respect to an optical system, a mechanism structure, and a controller circuit unit, a common use for both of a CD and an MO cartridge is realized as much as possible. Further, in recent years, a digital video disk (DVD) is also started to be spread and a common use for both of a DVD and an MO cartridge is also realized as much as possible in a manner similar to the CD.
In an optical disk drive using exchangeable media such as MO, CD, DVD, and the like, since a track eccentricity amount of a loaded medium is different every medium, the eccentricity amount of the medium is measured at a stage of an initializing process after the medium was loaded and an eccentricity offset current is supplied to a VCM synchronously with a medium rotation so as to set off the measured eccentricity amount. When tracks are regarded as straight lines, since the medium eccentricity draws a sine curve, what is called an eccentricity memory such as an RAM in which a sine value in which a rotational angle of a predetermined resolution is used as an address has preliminarily been stored is prepared, the eccentricity amount is obtained by reading out a corresponding cosine value from the eccentricity memory synchronously with an actual rotating position of the medium from an amplitude measured as eccentricity information and a phase for a rotational reference position, and an offset current is supplied so as to set off the eccentricity amount. In this case, in the MO cartridge, since the medium rotational speed is always constant owing to the constant angular velocity (CAV), it is sufficient to prepare one kind of eccentricity memory in which a sine value at each position in which the rotating position is used as an address has been stored.
In the media of a CD, a DVD, and the like, however, since a constant linear velocity (CLV) is used, the medium rotational speed has to be changed in order to keep a linear velocity constant in accordance with a position of an access track in the radial direction of the medium. When the rotational speeds are different in the radial direction of the medium as mentioned above, a time which is required for one rotation of the medium (rotational period) is also changed according to the rotational speed. A width of one address of the eccentricity memory has a value obtained by dividing the time required for one rotation by the number of addresses and the width of one address is changed depending on the rotational speed of the medium. Therefore, a plurality of kinds of eccentricity memories have to be prepared in accordance with the change in rotational speed of the medium and a capacity of the eccentricity memory is extremely large, resulting in a cause of disturbing a reduction in costs of the apparatus. Each time the medium rotational speed changes, different eccentricity memories have to be accessed, so that the number of accessing times of the memory also increases, resulting in an obstacle in realization of a high processing speed.
According to the invention, there is provided an optical storage apparatus which can efficiently correct an eccentricity by an access of an eccentricity memory of one kind even if a medium rotational speed is changed for a constant linear velocity (CLV).
According to an optical storage apparatus of the invention, a light beam from an optical unit is moved to a target track and is on-tracked by an access control unit provided for an MPU or the like by a driving control of a positioner using a VCM for moving a lens to irradiate the light beam onto a medium in the direction traversing medium tracks, and the optical storage apparatus further has a linear velocity control unit for variably controlling a rotational speed of the medium by a spindle motor in accordance with a radial position of the medium so as to set a linear velocity in the circumferential direction at the irradiating position of the light beam to a constant value. According to the invention, the optical storage apparatus is characterized by comprising: an eccentricity measuring unit for measuring an eccentricity amplitude (A) of one rotation of the medium and an eccentricity phase xcfx86 for a start position of one rotation; an eccentricity memory in which an area from the start position of one rotation of the medium to an end position is divided into a plurality of regions every predetermined rotational angle and addresses are sequentially allocated and a sine value of each rotational angle increased by every predetermined rotational angle is stored in each address; a read control unit for generating an address (a) in the eccentricity memory corresponding to the rotating position of the medium where the light beam is irradiated at present by using the start position of one rotation of the medium as a reference and for reading out a corresponding sine value sinea from the eccentricity memory by a designation of the address (a); and an eccentricity correcting unit for obtaining an eccentricity amount (L) on the basis of the sine value read by the read control unit and the measurement values measured by the eccentricity measuring unit and for controlling the positioner so as to set off the eccentricity amount (L). Consequently, it is sufficient to use one kind of eccentricity memory. Even when the medium rotational speed differs depending on the reproducing position in the medium radial direction because of the constant linear velocity (CLV), the sine value in the eccentricity memory corresponding to the present rotating position of the medium when the light beam is irradiated at present can be read out by accessing the eccentricity memory of one kind. A memory capacity of the eccentricity memory can be remarkably reduced and costs of the apparatus can be reduced.
The read control unit has: a rotational period detecting unit for detecting a medium rotational period (medium rotational speed) according to the position in the radial direction of the medium where the light beam is irradiated at present; a 1-address rotating time detecting unit for detecting a 1-address rotating time showing a medium rotating time of one address by dividing the rotational period by the number of addresses in the eccentricity memory; a medium present position detecting unit for detecting a medium present position showing the rotating position of the medium where the light beam is irradiated at present by using the start position of one rotation of the medium as a reference; and a memory reading unit for comparing an address upper limit value of the present read address in the eccentricity memory expressed by the 1-address rotating time with the present position of the medium where the light beam is irradiated at present, when the medium present position is less than the address upper limit value, for designating the same address (a), for reading out the sine value from the eccentricity memory, and when the medium present position reaches the address upper limit value, for updating to the address by adding xe2x80x9c1xe2x80x9d to the present address, and for reading out the sine value from the eccentricity memory.
More specifically, the rotational period detecting unit detects the number (X) of rotational period pulses showing the medium rotational period according to the position in the radial direction of the medium where the light beam is irradiated at present by counting sampling clock pulses of a predetermined frequency for one rotation of the medium. The 1-address rotating time detecting unit detects the number xcex94X of 1-address rotational pulses showing the medium rotating time of one address obtained by dividing the number (X) of rotational period pulses by the number (C) of addresses in the eccentricity memory. The medium present position detecting unit repeats the counting operation of the sampling clock pulses by using the start position of one rotation as a reference and detects the number cnt of pulses of the medium present position showing the medium rotating position where the light beam is positioned at present.
Further, the memory reading unit compares an address upper limit value xcex94X(a+1) of the present read address (a) in the eccentricity memory expressed by the number xcex94X of 1-address rotating pulses with the number cnt of pulses of the medium present position where the light beam is irradiated at present, and
I. when the number cnt of pulses of the medium present position is less than the address upper limit value, that is, when {cnt less than xcex94X(a+1)}, the same address (a) is designated and the sine value is read out from the eccentricity memory, and
II. when the number cnt of pulses of the medium present position reaches the address upper limit value, that is, when cnt=xcex94X(a+1), the address is updated to an address a=a+1 by adding xe2x80x9c1xe2x80x9d to the present address (a) and the sine value is read out from the eccentricity memory.
When detecting the number cnt of medium present position pulses indicative of the medium rotating position where the light beam is located at present, the medium present position detecting unit corrects the number cnt of medium present position pulses to a value without the eccentricity phase xcfx86 on the basis of the eccentricity phase xcfx86 obtained by the eccentricity measuring unit. Specifically speaking, the medium present position detecting unit converts the eccentricity phase xcfx86 measured by the eccentricity measuring unit to the number Xxcfx86 of eccentricity phase pulses expressed by a count value of the sampling clock pulses. When the number cnt of medium present position pulses is equal to or larger than 0 and is smaller than the number Xxcfx86 of eccentricity phase pulses (0xe2x89xa6cnt less than Xxcfx86), the value of cnt is corrected as follows.
cnt=(Xxe2x88x92Xxcfx86)+cntxe2x80x83xe2x80x83(1)
When the number cnt of medium present position pulses is equal to or larger than the number Xxcfx86 of eccentricity phase pulses and is smaller than the number (X) of rotational period pulses (Xxcfx86xe2x89xa6cnt less than X), the value of cnt is corrected as follows.
cnt=cntxe2x88x92Xxcfx86xe2x80x83xe2x80x83(2)
This phase correction indicates that the count value cnt of the medium present position pulses is corrected to a value corresponding to the address (a) of the eccentricity memory having no eccentricity phase.
The read control unit further has a linear interpolating unit for, when the medium present position where the light beam is irradiated at present is located in a portion within a predetermined rotational angle corresponding to the address (a) in the eccentricity memory, detecting a sine value of the medium present position by a linear interpolation of a sine value read from the eccentricity memory.
The linear interpolating unit designates the address (a) to which, for example, the medium present position where the light beam is irradiated at present belongs, reads out a sine value sinxcex8a from the eccentricity memory and obtains a sine value which was linear interpolated by the following equation when it is assumed that a rotational angle of one address is set to xcex94xcex8 and the number of pulses in one address indicative of a position in one address is set to (b).
sin xcex8a=sin xcex8a+sin xcex94xcex8xc2x7(b/xcex94X)xe2x80x83xe2x80x83(3)
When assuming that the sine value read by the read control unit is set to sinxcex8a and the eccentricity amplitude measured by the eccentricity measuring unit is set to A, the eccentricity correcting unit calculates an eccentricity amount (L) by the following equation.
L=Axc2x7sin xcex8axe2x80x83xe2x80x83(4)
When it is assumed that a rotational period at a reference position in the medium radial direction is set to the reference number Xr of rotational period pulses expressed by the count value of the clock pulses and the number of rotational period pulses indicative of a rotational period at a position in the medium radial direction where the light beam is located at present is set to (X), the eccentricity correcting unit corrects the eccentricity amplitude (A) to
A=A/(X/Xr)4xe2x80x83xe2x80x83(5)
and calculates the eccentricity correction amount (L).
That is, the eccentricity amplitude (A) is corrected so as to be inversely proportional to the square of a change amount from the reference rotational speed. It is now assumed that the VCM is used for correcting the eccentricity, an accelerating performance of the VCM is set to G, an angular frequency of the medium rotation is set to xcfx89, and an amplitude of an acceleration current for eccentricity correction is set to Ia. In this case, since the eccentricity amount (L) is equal to an amount corresponding to the integration of two times of an acceleration (Gxc2x7Iaxc2x7sinxcfx89t),
L=∫∫(Gxc2x7Ia/xcfx892)sinxcfx89txe2x80x83xe2x80x83(6)
Where, the eccentricity acceleration A=(Gxc2x7Ia/xcfx892).
Therefore, the eccentricity amount (L) is inversely proportional to the square of the rotational speed of the medium. Therefore, even if the rotational speed of the medium changes, as for the light beam as well, it is now assumed that, for example, a state where the light beam is set to the position of the highest rotational speed on the innermost side is labeled as a reference rotational speed, namely, the reference number Xr of rotation period pulses and a gain at this time is equal to 1. It is also now assumed that a gain correction coefficient {1/X/Xr)2} is inversely proportional to the square of a change amount from the referenced rotational speed. In this case, when a change in the number (X) of rotational period pulses at a position in the medium radial direction where the light beam is located at present is larger than the reference number Xr of rotational period pulses, the eccentricity correcting unit corrects the amplitude gain (G).
When the rotational period successively changes every rotation by controlling the light beam so as to be positioned on a medium track formed in a spiral shape, the read control unit obtains parameters necessary for reading out the eccentricity memory with respect to the first medium track and, after that, proportionally changes each parameter on the basis of the change in rotational period of one track, and performs the read control of the eccentricity memory. For example, when the rotational period successively changes every rotation by controlling the light beam so as to be positioned on the medium track formed in a spiral shape, the read control unit detects the number (X) of rotational period pulses by counting the sampling clock pulses with respect to the first medium track. After that, the read control unit changes the number (X) of rotational period pulses by every number of changed pulses of the rotational period of one track, thereby executing the read control of the eccentricity memory. Consequently, when the medium rotational speed successively changes, it is unnecessary to actually detect the rotational period after the second rotation and it is necessary to wait for a time of one rotation of the medium at most in order to actually measure the rotational period, so that a processing time can be reduced.
When the light beam is sought to the target track by an access control unit, prior to the start of the seeking operation, the rotational speed is changed to a rotational speed at which the linear velocity at a target track is made constant by the linear velocity control unit, a measuring process by the eccentricity measuring unit is performed in this state, and after that, the light beam is sought to the target track. As another form of the eccentricity correction upon seeking, when the light beam is sought to the target track by the access control unit, after the light beam was sought to the target track, the linear velocity control unit changes the rotational speed to a speed at which the linear velocity at the target track is made constant. In this state, the measuring process by the eccentricity measuring unit is performed. The medium rotational speed at which the linear velocity when the light beam is sought to the target track is constant is given from an upper apparatus.
Before the medium is loaded into the apparatus and the apparatus enters a ready state, the eccentricity measuring unit measures eccentricity information in a specific zone or an arbitrary zone of the medium. At this time, the eccentricity measuring unit measures the eccentricity amplitude (A) and eccentricity phase xcfx86 on the basis of a zero-cross point detection of a tracking error signal corresponding to a position in the direction in which the light beam formed on the basis of a photosensitive output of a medium return light obtained by the optical unit crosses the track in a state in which the driving operations of the carriage and lens are stopped. The eccentricity measuring unit obtains the eccentricity amplitude (A) by multiplying a track pitch to the half of the number (N) of zero-cross points of the tracking error signal of one rotation of the medium obtained by synchronizing with a rotation detection signal (index signal) indicative of one rotation of the medium and obtains a time required from a start position of one rotation of the rotation. detection signal to a middle point of the maximum zero-cross point interval time of the tracking error signal as an eccentricity phase xcfx86. The eccentricity measuring unit measures the number of zero-cross points of one rotation in an eccentricity correcting state by the eccentricity correcting unit based on the measured eccentricity information and, when the number of zero-cross points by the eccentricity correction exceeds the number of zero-cross points upon measuring, corrects the eccentricity phase xcfx86 obtained by the measuring process to an inverse phase. In this case, the eccentricity measuring unit corrects the phase to an eccentricity inverse phase (xcfx86+180xc2x0) obtained by adding the xc2xd rotational angle to the measured phase xcfx86 as an inverse phase. Further, the eccentricity measuring unit executes the measurement of the eccentricity information and the eccentricity correction after the measurement two times, respectively, and compares the numbers of zero-cross points of one rotation after the eccentricity correction. When a difference as a comparison result exceeds a predetermined threshold value, the eccentricity measuring unit repeats the measurement and correction of the eccentricity until the difference is equal to or less than the threshold value.
The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description with reference to the drawings.